This invention is directed to an electronic timepiece, and in particular to an electronic timepiece variable divider circuit for applying timekeeping signals to the smallest digit of time displayed having a frequency not evenly divisible into the frequency of the electronic timepiece time standard.
The accuracy and precision of electronic timepieces has been due in large measure to the accuracy of quartz crystal vibrators utilized as a time standard. Because the accuracy of a quartz crystal time standard is determined by the amount of deviation between a selected natural frequency of vibration and the actual frequency at which the time standard vibrates, considerable efforts are made during manufacture to minimize such deviation therebetween.
It has been found that the variance in accuracy of quartz crystal vibrators decreases proportionally with an increase in the number of quartz crystal vibrators having the same operating characteristics manufactured during a specific interval of time, such as a month. Accordingly, a natural frequency of 32,768 Hz(2.sup.15) has been selected as the operating frequency for optimizing natural frequency of the vibrator, such a natural frequency enabling divider circuitry comprised of N-series connected binary divider stages to be utilized to effect division of the natural frequency 2.sup.15 by 2.sup.N. Accordingly, in electronic timepieces operating in a timekeeping mode, the smallest digit of time displayed is seconds, and it is only necessary to divide the high frequency time standard signal produced by the oscillator circuit by 2.sup.15 to thereby apply a 1 Hz low frequency timekeeping signal to a counter having a display element associated therewith. Nevertheless, when a chronographic timekeeping mode is desired, a binary divider circuit capable of dividing the natural frequency 2.sup.15 Hz into a 1 Hz frequency signal, of the type utilized in timekeeping electronic timepieces is less than completely satisfactory. Although a time standard having a higher natural frequency than 2.sup.15 Hz can be utilized, because of the advantages which inure to manufacturing quartz crystal vibrators in bulk at the same natural frequency of vibration, such a solution is less than completely satisfactory. The other alternative is to utilize a binary divider circuit having a division ratio less than 2.sup.15. Nevertheless, because each of the digits of time less than one second have a decimal count, and require the input pulses applied thereto to have frequency of 10.sup.K, where K is a positive integer, the signal produced by a binary divider circuit cannot be utilized as an input to the lowest digit of time counters producing display signals.